Dead Horses - Discussion

"It is so written that it does not work that way. The End."

But that's not a fun way to spend the time between books.

Loren Pechtel wrote:And you just revealed that you're out there with military-grade equipment. Somebody's going to come have a look. If you want to maintain stealth you need to restrict yourself to passive sensors.

ThinksMarkedly wrote:Remember we were talking about a ship or ships that hypered in light-weeks to light-months out. The radar waves, which wouldn't be powerful enough to be detected at a distance anyway, travel at the same speed of the gamma ray beam that you're using as a weapon. The worst that would happen is that the target receives a packet of photons preceding the graser beam's arrival by a couple of minutes.

If you are a light-week out, then it takes a week (by definition) for your ranging pulse to hit the target and another week for the echo to get back to you, then another week for your graser shots to reach the target. What is your expected accuracy for anything not in a stable orbit?

The only way that the "couple of minutes" which you mention can happen is if you are a light minute from the target when ranging and firing.

Maybe that is why RFC does not write about graser shots from astronomical distances.

kzt wrote:I'm exceedingly impressed by how much David has maintained consistency and the world building, but there are points at which you just have to say 'umm, don't look behind this curtain.'

I must confess that while I am impressed that Weber understands the relationships between acceleration, time, velocity and position, I have issues. The Impeller Wedge doesn't just violate the laws of physics regarding conservation of momentum and energy, it rapes them. I can almost hear the screams in hyperspace of stars that are being murdered to provide the energy for those massive vollies of missiles.

Of course in the Honorverse, I don't look behind the curtain. I look under the skirt.

tlb wrote:If you are a light-week out, then it takes a week (by definition) for your ranging pulse to hit the target and another week for the echo to get back to you, then another week for your graser shots to reach the target. What is your expected accuracy for anything not in a stable orbit?

The only way that the "couple of minutes" which you mention can happen is if you are a light minute from the target when ranging and firing.

Maybe that is why RFC does not write about graser shots from astronomical distances.

You'd be right if that's what they were trying to do. The idea wasn't to use radar or lidar to range on your target, but on the multiple components of your weapon or sensor. The idea was to have a very long baseline interferometer telescope or something akin to it. In space, you're not limited in distance, so you can position your receivers many thousands of km from each other, up to a million, and have very, VERY accurate observation of things happening a light-month out.

The radar and lidar were supposed to be used to determine the accurate position vectors between those elements only. You don't need high-powered radar for that. A simple laser that people use today to bounce photons off the mirror on the Moon would suffice, I guess.

tlb wrote:If you are a light-week out, then it takes a week (by definition) for your ranging pulse to hit the target and another week for the echo to get back to you, then another week for your graser shots to reach the target. What is your expected accuracy for anything not in a stable orbit?

The only way that the "couple of minutes" which you mention can happen is if you are a light minute from the target when ranging and firing.

Maybe that is why RFC does not write about graser shots from astronomical distances.

ThinksMarkedly wrote:You'd be right if that's what they were trying to do. The idea wasn't to use radar or lidar to range on your target, but on the multiple components of your weapon or sensor. The idea was to have a very long baseline interferometer telescope or something akin to it. In space, you're not limited in distance, so you can position your receivers many thousands of km from each other, up to a million, and have very, VERY accurate observation of things happening a light-month out.

The radar and lidar were supposed to be used to determine the accurate position vectors between those elements only. You don't need high-powered radar for that. A simple laser that people use today to bounce photons off the mirror on the Moon would suffice, I guess.

That makes more sense for the comment about the "couple of minutes" between the ranging signal and the graser beam.

But assuming it is tried from a light week out as stated, it is still the case that this system is trying to hit something in a week's time based a brief measurement of its position and velocity from a week ago; that is still insane. That can only work foe something in a stable orbit around its sun; it would very chancy to try it on something in an unpowered orbit around an inhabited planet.

tlb wrote:
But assuming it is tried from a light week out as stated, it is still the case that this system is trying to hit something in a week's time based a brief measurement of its position and velocity from a week ago; that is still insane. That can only work foe something in a stable orbit around its sun; it would very chancy to try it on something in an unpowered orbit around an inhabited planet.

How big is the target? You get a whole lot more margin for error if it is kilometers across. From the right angle at the right time you’ll have a decent window to hit the target. Like you are in the same plane as the orbit and you target it during the window where it is mostly moving towards or away from you.

tlb wrote:But assuming it is tried from a light week out as stated, it is still the case that this system is trying to hit something in a week's time based a brief measurement of its position and velocity from a week ago; that is still insane. That can only work foe something in a stable orbit around its sun; it would very chancy to try it on something in an unpowered orbit around an inhabited planet.

I wasn't passing judgement on how insane or not that strategy would be. Only on the technical feasiblity of it.

Observing the target is one thing. Predicting where it will be in one week's time is another altogether. Some targets will have stable and predictable orbits, some will not. What's more, there's a question of whether anything would be in the way, like another ship.

tlb wrote:But assuming it is tried from a light week out as stated, it is still the case that this system is trying to hit something in a week's time based a brief measurement of its position and velocity from a week ago; that is still insane. That can only work foe something in a stable orbit around its sun; it would very chancy to try it on something in an unpowered orbit around an inhabited planet.

kzt wrote:How big is the target? You get a whole lot more margin for error if it is kilometers across. From the right angle at the right time you’ll have a decent window to hit the target. Like you are in the same plane as the orbit and you target it during the window where it is mostly moving towards or away from you.

Based on the sampling you have to acquire position, velocity and acceleration (which I left out before) to some very good precision, since you need to work out the orbit (including eccentricity) well enough to predict with high confidence the position in two weeks time. Suppose you want to hit the Blackbird base on the moon of a gas giant planet; then you will also have the same information for the planet, plus be able to predict the rotation of the moon (so you are not trying blast through the wrong part).

I am not going to say it impossible with good enough equipment, just that the technique is limited to targets whose position can be predicted with confidence after the time it takes for light to make a round trip. How much simpler is it to send it a stealth probe with a bomb attached?

Orbital data for most interesting objects will be easily available in navigational databases to milimeter accuracy. And you are not going to fire one shot and leave. You are goong to saturate the area to cover your error predictions. I have no real idea how fast rapid fire on a graser is, but lets assume two shots per second. You have say 20 weapons shooting at that rate for say 5 minutes, then you hyper out and await the tragic news to arrive. The odds are that you’ll get multiple hits, possibly a lot of hits, on a multi-km sized object and probably ruin a lot of people’s weekends.

Also to consider: just getting a low power graser hit is really bad if you are a mammal. Intense gamma rays are bad, and it doesn’t have to be nearly powerful enough to do any physical damage to a space raft to kill everyone inside.

tlb wrote:That makes more sense for the comment about the "couple of minutes" between the ranging signal and the graser beam.

But assuming it is tried from a light week out as stated, it is still the case that this system is trying to hit something in a week's time based a brief measurement of its position and velocity from a week ago; that is still insane. That can only work foe something in a stable orbit around its sun; it would very chancy to try it on something in an unpowered orbit around an inhabited planet.

Yeah, I have much less trouble with it now that I understand what he's trying to do. That doesn't mean it works, though--there's still a big problem. Assuming his satellites can do what he's imagining the graser will still be a certain miss.

The thing is, you need not only your location but velocity. If you fire at a target a light-hour away you need to know your velocity relative to the target down to several meters per hour.

Note that shooting at something orbiting a planet isn't going to be a problem. Fire only when the target is off to the side (by your viewpoint), if you have any chance of hitting your target you have basically zero chance of hitting the planet.